Silk screen stencil ink



ties, etc.

Patented June 12, 1951 UNITED STATES PAT ENT F F I CE SILK SCREEN STENCIL INK Howard A. Van Etten, Monroe, N. Y., assignor to E. I. -du Pont. de Nemours & Company, Wilmington, -D'el., a corporation of Delaware NoDrawing. Application February 13, 1948,

Serial No. 8,272

ii-Claims. (c1. 26028.5)

This invention relates to coating compositions "and particularly to coating compositions adapted fo application by means of a silk screen stencil and more particularly to those compositions emscreen or ground, consisting of silk, 'organdy, metal cloth, and synthetic fibers, such as nylon, polyethylene, etc.

The process :for' preparing the stencils consists of applying a coating of a light-sensitive substance adapted to be rendered insoluble upon exposure to light, on a woven web, exposing the light-sensitive coating to light transmitted through a print of the pattern to be reproduced and dissolving and removing the coating from the web not rendered insoluble by light.

Paints, inks or-other printing media are'forced through that portion of the stencil not coated with the insoluble coatingby means of a'squeegee and deposited on the surface to be decorated, thus forming a facsimile of the original design. The method is "known'as the silk screen process because originally silk was exclusively employed for the screen base.

This processhas been employed for decorating many-surfaces and has'been developed to a high state of efficiency. It has been necessary to develop different inks for the various surfaces decorated to insure proper adhesion of the ink to the surface. Recently, polyvinyl chloride and vinyl chloride-acetate=copolymer resin coatings have been introduced for a wide variety of uses and have been accepted in view of their superior quality 'over'many other types of coatings formerly used. For many uses the polyvinyl chloride resin coatings require decoration, particularly coated fabrics and unsupported films designed for use as upholstery, tablecloths, novel- For printing or stenciling polyvinyl chloride resin surfaces, it is desirable to employ inks which contain a polyvinyl chloride resin binder to assure anchorage-of the printed design to the base.

The consistency of the composition for satisfactory use as a stencil ink must be "such that the materialwillleave an even, sharply defined surface when dried. nature and must' break'cleanly from the design without stringing when the stencil is removed. For stenciling continuous sheet material, it is necessary that "the solvent evaporate before batching the material in roll form. The drying It'must 'not be sticky in of the ink is usually carried out by passing the material through a heated tunnel. The {rate at which the solvent evaporates from the .stencil ink is very important. If thesolvent evaporates too rapidly, the stencil will become clogged with partially dried ink. Once a quantity of ink is placed on a stencil screen, it should not change in either its consistency or its property to break away sharply from the stencil when the stencil is removed from the surface being decorated.

It is an object of this invention to provide a vinyl resin stencil sink for use in decorating vinyl resin coated fabrics. .A further object is to provide a vinyl resin stencil ink which will permit the screen to release readily .from the surface being decorated and .not form legs or develop stringiness when thestencil is pulled awayirom the surface being stenciled. .A.still further object is to provide a'vinyl resin stencil inkwhich will notchange in consistency when being moved back and forth across a silk screen stencil by means of alsqueegee in a continuous stencil operation. Othe important objects will be'readily apparent as the description of the invention proceeds.

' The objects of this invention are accomplished by incorporation of wax into a'composition comprising a soluble vinyl resin, pigment, solvent Example 'I A red stencil ink was prepared by first dis solving the vinyl resin binder in hot methyl ethyl ketone as per the following formula:

Per cent Polyvinyl resin Methyl ethyl ketone '75 llho polyvinyl resin used in this example was amultt polymer. the approximate composition of which may vary within the following limits:

' to by Weight .of .combined vinyl chloride. 19.7% to 7.0% by weight .of ,combinedwrinyl-acetate. 0.3% to 3.0% by weight of maelic or similarnlphzibeta olefinic unsaturated carboxylic acid.

.3 The following ingredients were premixed before grinding on a three roll paint mill:

Wet l7 ry PCI'LTJl! 25% solution polyvinyl resin in methyl ethyl ketone, supra 15.40 Cadmium sulfidered pigmen *5. 2O 72. Polypropylene glycol sehacate. 6. 38 l0. 60 Methyl ethyl ketone 9. 82 .i 20% dispersion of paraffin wax in toluol i. 20 l. ()0 Malic acid U .60 1.00

Example II A stencil ink was prepared using a resin different from that disclosed in Example I, as indicated below:

Per cent copolymer of vinyl chloride and vinyl acetate in the approximate ratio of 85:15 Ethyl acetate 80 A suitable copolymer resin for use in this ex ample may be obtained on the open market under the trade name of Vinylite VYI-II-I, which is sold by Carbide & Carbon Chemicals Corporation.

The following ingredients were thoroughly mixed before grinding on a three roll paint mill:

Wet Dry Per sen! Per cent solution of copolymer of 85 vinyl chloride and l5 vinyl acetate in ethyl acetate supra 15.10 Cadmium su1fidercd pigment 72. Polypropylene glycol sebacate. 5. ll. 10 Methyl ethyl ketone 8. eeeeee 20% dispersion of paraffin wax in toluolfli 2. 1,20 Ethyl acetate 13.50

Example III A blue stencil ink was prepared as follows: Per cent 25% solution of vinyl resin referred to in Example I in methyl ethyl ketone 36.6 Blue pigment-copper phthalocyanine 3.9 Barytes 40.9 Dioctyl phthalate 6 .5 Malic acid 1.0 Methyl ethyl ketone 9.7 20% dispersion of parafiin wax in toluol 3.2

A complete breakdown of the above is as fol-- lows:

Wet Dry Per cent Per cent The stencil ink of this example was prepared in the same manner as described in Example I.

The stencil inks of Examples II and III were employed for decorating polyvinyl chloride coated fabric as described in Example I. The designs formed had sharp definition, and there was substantially no tendency for the silk screen to adhere to the surface being decorated when it was pulled away. Also, there was little or no tendency for the ink to thicken and clog the silk screen stencil interstices through which the ink is forced by means of a squeegee.

Compositions having the same formulae as those described in Examples I, II and III, except that the paraffin wax was omitted, were prepared and employed as stencil inks for polyvinyl chloride resin coated fabric in the manner described above. The silk screen could not be readily separated from the surface being decorated and the ink formed legs when the silk screen was pulled away and did not form a cleancut and well defined design. Also, the ink clogged part of the openings in the silk screen stencil after it was drawn back and forth over the screen by a squeegee a relatively few times The vinyl resin for use in practicing this invention must be sufficiently soluble in relatively low boiling solvents, such as, e. g., methyl ethyl ketone, that a 20-25% solution will form a free flowing liquid at room temperature. The copolymers of vinyl chloride with vinyl acetate, ethyl fumarate, vinylidene chloride, etc. are satisfactory, particularly where the vinyl chloride represents -90% of the polymer. As indicated in Example I, such copolymer resins may be modified with a small amount of polycarboxylic acid.

It will be noted that in Example II the resin is first dispersed in ethyl acetate which does not have as great a solvent action on the resin as methyl ethyl ketone. This results in a composition which is somewhat short or apple saucy. This is an advantage and represents the preferred embodiment since the inks made with the resin dispersed in ethyl acetate are of a mayonnaise consistency and have less tendency to flow around the edges of the squeegee during application and also less tendency to leak through the openings in the stencil screen unless pressure is applied.

There is considerable latitude in choice of pigments for this invention. In the case of solutions of the vinyl chloride vinyl acetate-maleic acid multipolymer, the presence of unreacted carboxyl groups results in a tendency toward reactivity with basic pigments which results irgelling of the solution. This gelling is overcome or prevented by the presence of small amounts of acidic or basic substances. The use of malic acid together with other organic acids with dispersions of multipolymer of vinyl chloride, vinyl acetate and maleic acid in the presence of basic pigments to prevent gelation is disclosed and claimed in copending application Serial No. 770,- 195, filed August 22, 1947, by H. T. Doderer, now abandoned.

Where stain resistance is required for certain application of the coating, such as, e. g., table cloths, wall coverings, aprons, etc.; a non-migrating type of plasticizer, such as polypropylene glycol sebacate and polypropylene glycol adipate, as wall as other polyesters, is required, since it has less. afiinity for various stains. Where stain resistance is not important, other plasticizers oi the monomeric ester type may be used, such as,

V e. g., dioctyl phthalate, tricresyl phosphate, dibutoxy ethyl phthalate, dibutoxy ethyl sebacate, etc.

In order to obtain sumcient coverage of the base coating in one application of the stencil ink, the pigment content should not be less than 60% of the total solids of the ink. The maximum amount of pigment which can be employed is 80% of the total solids. The specific choice of pigment will determine the preferred amount, since oil absorption, covering power, efiect on film strength, etc., vary with difierent pigments. The ratio of pigment to binder and plasticizei' in the composition of this invention is considerably higher than normally employed for coating compositions.

The high percentage of pigments in the stencil paste of this invention does not permit the composition to be prepared by conventional methods, such as, e. g., dissolving the binder in an organic solvent, separately grinding the pigments in plasticizer, then combining the binder solution with the pigment-plasticizer mixture. Due to the low ratio of liquid ingredients to the pigment, it is necessary to first dissolve the binder in an organic solvent, then add the dry pigment and plasticizer to the binder solution, after which the entire composition is ground on a three roll paint mill. In practice the stencil inks of this invention are usually coated over with a clear (nonpigmented) solution of vinyl resin to prevent the pigment particles from being abraded off in service.

As indicated above the presence of a small amount of a wax is essential in the composition of this invention. Inks containing as little as 0.5% of wax and those containing as high as 5% based on the total non-volatile content of the ink have been found useful. Approximately 1%, based on the non-volatile content, is the preferred amount of wax. Paraffin wax is preferred due to its solubility in volatile organic solvents.

The compositions of this invention are designed specifically for application by means of r silk screen stencil. They are also useful as printing inks for application by means of intaglio print rollers. For application by means. of intaglio print rolls the compositions described in the examples should preferably be diluted somewhat with the volatile solvent.

It is apparent that many widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, and therefore, it is not intended to be limited except as indicated in the appended claims.

I claim:

1. A stencil ink having the following composition by weight:

6 g Per cent 25% solution of a copolymer of 85% polyvinyl chloride and 15% polyvinyl acetate 2. A stencil ink of claim 4 consisting essentially of a polyvinyl chloride-polyvinyl acetatemaleic acid resin, 1% maleic acid, from to pigment, from 0.5% to 5.0% wax all based on the non-volatile content of the ink.

3. The product of claim 4 in which the polyvinyl resin is a copolymer prepared by polymerizing a monomeric mixture containing vinyl chloride and 15% vinyl acetate.

4. A stencil ink comprising a vinyl resin, plasticizer, wax, pigment and a mixture of volatile solvents for the said resin and wax, the said pigment being present in amount between 60% and 80%, the wax being present in amount between 0.5% and 5.0% both based on the weight of the non-volatile components of the ink, the balance of the non-volatile portion being a resin polymerized from a mixture of 80% to vinyl chloride, up to 3% of maleic acid and the balance being vinyl acetate, a 20% to 25% solution of the resin in methyl ethyl ketone being free-flowing liquid at room temperature.

HOWARD A. VAN ETTEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,073,229 Shuey Mar. 9, 1937 2,254,072 Jenkins Aug. 26, 1941 2,264,625 Doolittle Dec. 2, 1941 2,268,595 Huber et a1 Jan. 6, 1942 2,391,621 Powell et al Dec. 25, 1945 OTHER REFERENCES Fligor et al.: Ind. and Eng. Chem, vol. 3'7, No. 5, May 1945 (pp. 504-508).

Ellis: Printing Inks (Reinhold Pub. 00.), 1940, page 116.

Wolfe: Printing and Litho Inks. (MacNair- Dorland), 3rd ed., 1941, page 291.

Pollack: Plastics, January 1946, pp. 35-38 and 123. 

4. A STENCIL INK COMPRISING A VINYL RESIN, PLASTICIZER, WAX, PIGMENT AND A MIXTURE OF VOLATILE SOLVENTS FOR THE SAID RESIN AND WAX, THE SAID PIGMENT BEING PRESENT IN AMOUNT BETWEEN 60% AND 80%, THE WAX BEING PRESENT IN AMOUNT BETWEEN 0.5% AND 5.0% BOTH BASED ON THE WEIGHT OF THE NON-VOLATILE COMPONENTS OF THE INK; THE BALANCE OF THE NON-VOLATILE PORTION BEING A RESIN POLYMERIZED FROM A MIXTURE OF 80% TO 90% VINYL CHLORIDE, UP TOP 3% OF MALEIC ACID AND THE BALANCE BEING VINYL ACETATE, A 20% TO 25% SOLUTION OF THE RESIN IN METHYL ETHYL KETONE BEING FREE-FLOWING LIQUID AT ROOM TEMPERATURE. 